SOLVED

After removing the CMOS battery in addition to the main battery, and powering the laptop on it worked. After, I readded both batteries and it now continues working. Maybe I should replace both batteries to avoid that happening again in the future?

Thank you very much for your support!

https://monyet.cc/comment/1875010

Yesterday I was using my Lenovo Ideapad laptop until the screen went totally black, but it was still on as the led's light was on. 1 or 2 minutes gone by with me trying to press keys for brightness etc, and then it suddenly shutdown. Afterwards trying to turn it on again, the led will bright for 2 seconds until it shuts itself down...

I tried removing and putting the battery again to no luck.

First I thought it could be the CPU/iGPU, now maybe the battery or motherboard is the issue? I repaired this latop many times, but this is the first time this happens, so I don't know what it can be..

Apart from an old and low-end smartphone I'm using to write this, this is the only computer I own.